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ReZ ReZ is offline
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Cruising - computer shut down - back online - WTF?

1985.5 late 944. 249,000 miles and counting.

Not a chronic problem, just a random problem.

The car shuts down while cruising, then comes back onling a few seconds later. This has never happened upon full acceleration.

Example with details:

On the freeway in 5th gear @ 80 MPH. Cruising. All of a sudden, no power, tach bounces from 3K down to zero and back around in between that area of 0-3K. this happens for like 2-10 seconds. Then, the car is back online! Cruising like nothing happened. This is at random. Not chronic.

This has happened several times. I want to solve this annoying problem.

Other times are on decel, and it just bucks for a brief second when I get on the throttle lightly. It doesn't shut down when it does this. It's at random. Not chronic.

NOTE: when the tach freaks out on the shut down, the speedo freaks out and drops too. Fuel, oil, and voltmeter are ok and read normal during the shutdown period. The shutdown period is at random, not me doing it.

I'm thinking RPM related between 2K RPM and 3.5K RPM for shutdown. But for the spontaneous buck, who knows. I think they are related. I BET GROUND! or that DME!

I have replaced the main spark plug wire from the coil to the cap. Cap and rotor are replaced with OEM ones. Spark plugs are a few thousand miles old. All OEM. No aftermarket crap.

Things I would like to check:
-That DME thing you guys talk about
-Engine grounds, maybe add a few more extras. (Where are these grounds? I'll just look visually)
-Air Flow Meter scratching? It's not consistent, so I donít' see how it's bad...
-Computer resetting for no unknown reason? Bad computer ground?
-Ignition switch? Perhaps a loose "on" position.
-Bad inlet duct from the Air Flow meter to the intake runners?
-Would a vacuum leak cause a surge on cruise?
-Bad igniter coil?

No cranking problems. This car has run flawless for over 100,000 miles. I have never been stranded.

I have the performance chip sitting around from weltmeister, but haven't put it in since this problem has beem happening at random. I'll drive for 75+ miles with no problems. THen the next time I run it, bam it happens. But when it happens, it like in waves. If it does it once in a drive, it happens like 2-3 times over 50 miles.... It sucks. I don't know whether to pull over or not! Then she comes back online! lol.

Anyone have this problem? It's a weird one.


Thanks!
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-1985.5 944 (late)
-1974 914
-1990 RX7 TII
Old 06-09-2004, 02:00 AM
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Old 06-09-2004, 12:25 PM
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Ingition switch.
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Old 06-09-2004, 05:01 PM
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ReZ ReZ is offline
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So you are suggesting a loose wire in the ignition switch?

I'll check it out.

I'm thinking the ignitor coil if it's not the switch.
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It's all about the corners!
http://www.calinetworks.net/rez/redt2/7n914pictar.gif

-1985.5 944 (late)
-1974 914
-1990 RX7 TII

Last edited by ReZ; 06-09-2004 at 09:58 PM..
Old 06-09-2004, 09:54 PM
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I agree, look at the ignition switch and also consider replacing your DME relay (good rpeventative maintenance, and you can keep the old one as a spare).
Also check out this thread....the exact cause of your problem might be different, but a good read for electrical probs:
Engine cutting out when I turn right....
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1989 Porsche 944, 1973 VW Beetle - gone but not forgotten
Old 06-10-2004, 05:09 AM
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ReZ ReZ is offline
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Exclamation

The problem is still here...

Things I have done:

-Replaced the ignition switch with a new OEM one & sprayed contact cleaner on the female harness attachment.

-Replaced the DME relay with a new OEM one.

-Cleaned the battery terminals really good and sprayed some contact cleaner on them.

------------

Note: The tach wants to drop to zero when the ignition system does a shut down spontaneously while in gear going at any speed. The 944 even does a slight stumble and sometimes shuts off when idling. But she idles perfectly when she doesnít freak out!!!

So.... I am starting to run thin on ideas to fix this problem!

-Replace Igniter coil ?
-Replace computer ?
-Add a ground from the engine to the chassis? (Where's a good spot?)
-Check computer ground?
-Air Flow Meter? Clean the electrical with contact cleaner?

Drive it off a cliff and claim insurance?

Anyone's help would be greatly appreciated.

HELP!!!
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It's all about the corners!
http://www.calinetworks.net/rez/redt2/7n914pictar.gif

-1985.5 944 (late)
-1974 914
-1990 RX7 TII
Old 07-09-2004, 10:42 AM
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ReZ ReZ is offline
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Ignitor coil replaced. Problem is still here.
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It's all about the corners!
http://www.calinetworks.net/rez/redt2/7n914pictar.gif

-1985.5 944 (late)
-1974 914
-1990 RX7 TII
Old 07-09-2004, 01:10 PM
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ReZ ReZ is offline
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Well, I found out some RATS chewed my vaccum lines.

The one running to the pressure regulator to the pressure dampner, and the one right after the air mass sensor.

diagram of lines.

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It's all about the corners!
http://www.calinetworks.net/rez/redt2/7n914pictar.gif

-1985.5 944 (late)
-1974 914
-1990 RX7 TII

Last edited by ReZ; 07-09-2004 at 02:26 PM..
Old 07-09-2004, 02:24 PM
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Bad DME.

gb
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Old 07-09-2004, 03:03 PM
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ReZ ReZ is offline
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Quote:
-Replaced the DME relay with a new OEM one.
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It's all about the corners!
http://www.calinetworks.net/rez/redt2/7n914pictar.gif

-1985.5 944 (late)
-1974 914
-1990 RX7 TII
Old 07-09-2004, 03:08 PM
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No, not a bad DME relay, a bad DME.

There is a world of difference. The DME relay provides power to both the DME and the fuel pump.

The DME is the computer, the brain of the Motronic system, and if it is bad, you get no spark or no fuel or neither, and it can be intermittent.

gb
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Good luck, George Beuselinck
www.944ecology.com
Porsche Deconstructor (tm)
We buy 944s and sell 944 parts (845-379-1944)
We rebuild torque tubes and instrument clusters for 944/968/928
Old 07-09-2004, 03:35 PM
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ReZ ReZ is offline
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Vaccum lines replaced with silicone blue.

Well, the car is idling for over 20 minutes with no cutting out. Time for a test drive.
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It's all about the corners!
http://www.calinetworks.net/rez/redt2/7n914pictar.gif

-1985.5 944 (late)
-1974 914
-1990 RX7 TII

Last edited by ReZ; 07-09-2004 at 04:59 PM..
Old 07-09-2004, 04:50 PM
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Check if one of your battery terminals isnt accidentally touching the hood.

That happened to me..car kept shutting off, and i could never figure out why..

then i saw the burn mark on the hood on the inside.
Old 07-09-2004, 11:17 PM
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ReZ ReZ is offline
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Well, the car runs much better. It doesn't completly shut off now. It just hiccups, like a quick buckevery once in a while. It does this while idling or cruising. I'm going to recheck the vaccum lines and see if I missed anything or some old lines migh have small cracks that would cause leaks.

Other than that, I do not know. I'll check the battery for contact, but I doubt that's it...
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It's all about the corners!
http://www.calinetworks.net/rez/redt2/7n914pictar.gif

-1985.5 944 (late)
-1974 914
-1990 RX7 TII
Old 07-10-2004, 01:50 PM
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Correct me if I'm wrong but is that a rotor from a rotary as your picture?
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Old 07-13-2004, 07:52 PM
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